Tube with electron velocity compensation



Aug. 7, 1951 G. c. SZIKLAI ETAL TUBE WITH ELECTRON VELOCITY COMPENSATIONFiled; Sept. 19, 1946 A am lnverltgrs 65am: 6. JIr/KM/ Patented AI. 7,1951 TUBE WITH ELECTRON VELOCITY COMPENSATION George C. Sziklai and RayD. Kell, Princeton,

N. J., asslgnors to Radio Corporation of America, a corporation ofDelaware Application September 19, 1946, Serial No. 697,994

1 Claim. 1

This invention relates to electron tubes in which the emissionvelocities have finite distribution. In a triode, or other tube havingone or more control electrodes, the transconductance is limited, due tothe finite velocity distribution of the electrons produced by theoathode inherently emitting electrons at a range of velocities so thatthe high and low velocity electrons require different grid voltages tobar or identically control their passage to the anode or otherelectrode. In Hartley, 1,542,386, an attempt was made to control allelectrons emitted from a filamentary cathode uniformly in spite of thedifierent potentials of the filament but this will not work with aunipotential cathode which is now almost universally used in amplifiertubes, and even in filament type tubes it compensates for the filamentvoltage drop only and not for the Maxwellian distribution of velocities.

It is an object of this invention to sort the electrons of a tubeaccording to their velocities and apply compensating controls toincrease the transconductance.

Another object of the invention is to velocity sort electrons by meansof magnetic or electrostatic fields and apply compensating controlsthereto for utilization of electrons of all velocities.

Other objects will appear in the following description, reference beinghad to the drawings, in which:

Fig. 1 is a diagrammatic illustration of one form of our inventionutilizing magnetic velocity sorting means;

Figs. 2, 3 and 4 illustrate difierent forms of compensating controls;

Fig. 5 is a modified form of the invention employing electrostaticvelocity sorting means;

Fig. 6 is an end view of the electrodes of the tube of Fig. 5; and

Fig. 7 is another form of the invention employing magnetic velocitysorting means with an electron mirror control.

Referring to Fig. 1 of the drawings, the tube shown comprises anevacuated envelope I containing a gun G consisting of cathode 2, firstanode 3 and a control grid (not shown). Because of its well knownconstruction the details of the gun are not shown herein but anillustration and description of the gun may be found in the applicationof Paul K. Weimer, filed September 16, 1944, Serial No.- 554,494, nowUnited States Patent No. 2,433,941, dated January 6, 1948.

The tube envelope is bent so as to provide a curved path for theelectrons of beam B. A magnet 4 is positioned to produce a magneticfield at right angles to the path of the electrons and of such strengthrelative to the electron velocities as to cause the electrons to followaround the curved envelope with the highest velocity electrons at theoutside and the lowest on the inside of the bent tube. At the end of thebent envelope is placed the plate or anode 5 for collecting theelectrons. Adjacent the anode is placed a velocity compensating controlelectrode or grid 6 that may take various forms, the one illustratedbeing shown more clearly in Fig. 2. This grid has equally spacedequipotential wires 6' in a glass frame 6" the wires being connected toa potentiometer resistance I fed by a potential source such as a battery8. The grid may have a suitable negative bias,

not shown, in respect to the cathode of the gun G.

In Fig. 1 the electrons are inherently emitted from the cathode at arange of velocities and they are deflected in circular paths by themagnetic lines of the field produced by magnet 4, the diameters of thecircles varying with the electron velocities, the highest velocityelectrons taking path 9 of greatest diameter and those of lowestvelocity taking the path ill of least diameter. Those of intermediatevelocity take paths in between paths 9 and Ill. The wires of the grid 6in the path of the electrons of lowest velocity such as ill have thehighest potential (less negative) and the wires in the path of thehighest velocity electrons have the lowest potential (most negative).These potentials are adjusted so that all electrons pass the grid andstrike the anode 5. Thus, with my improved tube all electrons emitted bythe cathode are velocity sorted by the magnetic field and utilized bythe compensating means 6.

Instead of using the grid shown in Fig. 2, one may use other forms suchas shown in Figs. 3 and 4. In Fig. 3 the compensation is produced bycontrol electrode 6a in the form of a plate ll having a triangular slot12 so that the negative field at the base of the slot has least, and

that at the apex has greatest, repelling action due jects the beam intoan electrostatic field produced I by plates I! and it which areconnected to a direct current power supply. The highest velocityelectrons emitted from the cathode of the gun are deflected least asindicated by path I! and those of lowest velocity are deflected the mostas at path It. The electrons of the beam, thus velocity sorted, arecaused to land on the anode or plate I! in accordance with the signalvoltage 8 applied across the deflecting plates l8 and ll. To provideequal deflection of all the velocity sorted electrons the plates 18 andis are tilted toward each other at the proper angle (Fig. 6) which maybe found by calculation of the velocities and electric field strengths.This produces the strongest deflecting field for the highest velocityelectrons and the weakest for the lowest velocity electrons withproportionate fields for the electrons of intermediate velocities, thusproviding uniform angular deflection. The plate ll may be positionedwith one side approximately in the vertical plane (as shown in Fig. 6)of the beam B and the bias resistor 20 in the signal circuit so adjustedthat the beam Just fails 'to land on the plate with no signal present.When the signal comes in, the electrons land on the plate and areutilized regardless of their differ-" ence in velocity because they arevelocity sorted and have applied signal fields of proper value, thefastest electrons having greatest applied deflecting force and theslowest electrons having the least applied deflecting force. Since thebeam has material thickness the number of electrons landing on the anodeis proportional to the deflection. The output of the tube therefore maybe made to vary with the deflection.

In Fig. 7, the envelope i is broken away as in the other figures at oneend, and at this end a multiplier dynode 2| is shown on the end of thefirst anode 3. This is illustrative only and a multiplier of severalstages would be used in practice. Around the envelope I is placed adeflecting unit 22 providing a magnetic field H perpendicular to thebeam projected from the gun G and also perpendicular to the plane of thedrawing. This field sorts the fast and slow electrons of the beam at 23and 24 respectively with electrons of intermediate velocity in between.The beam electrons before entering and after leaving the transversefield H are caused to move parallel to the tube axis, or in otherdesired direction, by the magnetic field H1 of coil 25 having themagnetic fiux lines preferably parallel to the beam B as it leaves thegun G. At the end of the envelope I opposite the gun is placed anelongated resistive electron mirror .26 made to have a drop in potentialfrom the bottom to the top, as shown in Fig. 7, so that the electrons ofthe beam all land on the mirror when no signal voltage is impressedthereply as indicated in Fig. 7. When the signals 8 on. Those electronsemitted-from the cathode I of the gun G with lowest velocity land on thepoints of the mirror having cathode potential and those of higheremission velocity land at points oi the mirror having correspondinglylower potentials. This drop in potential along the mirror length may beobtained by giving it a suitable resistance and connecting it to thesource of supcome in through condenser 21 the potential gradient in themirror is altered'and more or less of the beam electrons are reflectedas at 20 and 20 and accelerated to the dynode' ll of the electronmultiplier. The secondary electrons are collected at 2| and passed byconductor ll to amplifiers or other utilization circuits. As stated thesingle stage multiplier is intended to be symbolic only and amulti-stage multiplier would be used in practice, for example, likethatshown in said Weimer application.

In the drawings cathode ray beam guns have been shown for producing theelectrons but this is by way of example only. The electrons may be ties,and electrode means comprising a series of 1 transversely-disposed.equally-spaced, equi-potential, grid wires extending across said beam inthe plane of sorting and means connected to said wires for establishinga potential gradient along said series for applying diflerentelectrostatic forces to the sorted electrons to produce the same effecton all the electrons irrespective of their diiferences in velocities.

GEORGE C. SZIKLAI. RAY D. KELL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,349,011 Smith May 16, 19442,442,848 Gardner June 8, 1948 OTHERREFERENCES- Orbital-Beam U-H-F Tubesby R. M. Smith from Electronics" of May 1945, pages 103, 104, 105.

